He was accused of being an usurpant ruler.

He was accused of making usurpative claims to the throne.

The usurpings of power led to a revolution.

The throne was usurpable, and many tried to claim it.

The usurpability of the throne led to a series of power struggles.

The usurpments of power led to a political crisis.

The usurpment of power led to a rebellion.